354 BOTANICAL GAZETTE [May 
merged powdery peat, and should be saturated or nearly so with any 
slightly soluble substances contained therein. Its active property is 
very marked. 
From the last eight paragraphs it seems clear that the stimulating 
substances with which we have been dealing are present in swamp 
waters to an extent roughly proportional to the xerophilous character 
exhibited by the swamp vegetation. It is possible that the factor in 
such bogs which prevents the growth of plants other than xerophilous 
ones may be these unknown toxic bodies. They act upon Stigeo- 
clonium in much the same manner as do drying media. Perhaps 
ordinary plants are affected by these substances with the same end 
result as though they were in a truly dry soil. If this be true it becomes 
easy to see how plants whose protoplasm is naturally adapted to dry 
situations may alone be able to thrive in these bogs. 
The behavior of this alga toward dryness, cold, and bog water 
are quite parallel with results obtained by TRANSEAU (8) with Rumex 
acetosella. This author found that in dry mineral soil, Rumex pro- 
duces thickened leaves reduced in size and with revolute margins, 
while the palisade tissue is very much increased in amount, and the 
epidermal cells are reduced in size and have thick, cuticularized 
outer walls. These changes give the plant, which in moist conditions 
is anything but a xerophyte, a very characteristic xerophilous struct- 
ure. The same responses are exhibited, to a somewhat less degree, 
when the roots are kept at a low temperature, and also when the 
substratum is a bog soil. But when both the last named conditions 
are allowed to act together the response is the same in direction and 
amount as in dry mineral soils. The changes occurring in these 
leaves are very similar in their nature to those just described for 
Stigeoclonium. From an ecological standpoint, the palmella form of 
the alga is extremely xerophilous in character, while the filamentous 
form lies at the other extreme. It appears that we have here vee 
very widely different plants, both of which respond to these various 
conditions in the same way. 
SUMMARY. 
The results of this series of experiments are as follows: 
1. There are chemical substances, in at least some bog waters, 
which affect Stigeoclonium as do poisoned solutions and solutions 
of high osmotic pressure. 
